This invention relates to novel vinylidene fluoride-based fluoroelastomer compositions that exhibit little tendency to foul molds, i.e., minor or no mold deposits are formed after repeated moldings in the same mold cavities.
Fluoroelastomers may be cured with combinations of polyhydroxy compounds, typically difunctional phenol compounds, as the crosslinking agent and quaternary phosphonium or tetraalkyl ammonium salts as accelerators, as is described in U.S. Pat. No. 3,655,727 to Patel and in U.S. Pat. No. 4,496,682 to Schmiegel. The chloride and bromide salts of the phosphonium or ammonium accelerators are most commonly used and the fluoroelastomer compositions usually include metal hydroxides and metal oxides as acid acceptors for the curing formulation. However, the manufacture of molded products from these compositions presents a serious problem because, in spite of the fact that mold release agents are sprayed into the mold cavity to coat the mold cavity surface or release agents are incorporated in the polymer, the vulcanizates tend to adhere to the walls of the mold cavity. After only a few mold cycles heavy black deposits are formed on the walls of the mold. These deposits can have a serious adverse effect on the quality of the molded articles so that reject losses and major downtime incurred for mold cleanup add materially to the cost of manufacture of the fluoroelastomer article. Thus, there is a need in the fluoroelastomer art for compositions that can be molded repeatedly, in the same cavity, without the formation of dirtied or fouled mold surfaces.